The present application is a continuation of International Application No. PCT/SE01/00235, filed Feb. 8, 2001, which claims priority to Swedish Application No. 0000418-4, filed Feb. 9, 2000.
1. Technical Field
The present invention relates to a method and arrangement for measuring surface irregularities of an object. More specifically, the invention relates to a method and arrangement for measuring surface irregularities of an object by utilizing strobe lighting and photometric stereo.
2. Background Information
A method for topography measurement on flat objects by means of directional illumination is previously known from xe2x80x9cOptronik nyheterxe2x80x94TopografimAtning med strykande belysningxe2x80x9d, June 1999.
In those cases where the object to be measured is not flat, but instead exhibits a three-dimensional geometry, topography measurement cannot be applied by means of direct directional illumination.
The present invention provides an arrangement and method for measuring surface irregularities of an object where the object is illuminated by a source of light from a first position at a small angle of incidence. In this manner, measurement of an object exhibiting a curved, three-dimensional geometry is made possible.
This object is achieved by means of an arrangement comprising a pattern projector that generates a pattern matrix on an object and an evaluator arranged to measure the shape of the object based on the projection of the pattern matrix on the object. The evaluator is able to utilize information about the shape of the object calculated from the projection of the pattern matrix when determining the surface microstructure of the object.
The object is further achieved by means of a method comprising projecting a pattern matrix on an object by means of a pattern projector, measuring the shape of the object by an evaluator based on the projection of the pattern matrix on the object, and determining the surface microstructure from information about the projection of the pattern matrix on the object and shadow formations.
By generating a pattern matrix by means of a pattern projector, information about the shape and location of the object in relation to the pattern projector and camera is created. A useful pattern for this application is a gridiron pattern which is projected on the object. The projection of the pattern on the object describes the surface and position of the object, wherein the size of the squares can be utilized for determining the distance from the projector, and the deviation from linearity determines the shape of the object. When the shape and position of the object are known, the evaluating means determines the surface micro structure of the object.